In the usual type of known slide valve for controlling fluid flow, a movable slide block has a port which can be moved into alignment with a port in a stationary valve block. In order to keep the valved fluid from leaking, the blocks must be urged together with sufficient force to retain the fluid at the interface between the relatively movable blocks. However, if the retention force is high, a relatively large force is required to shift the movable valve block. There is an important need to minimize the required amount of shifting force, particularly in the case of valves of the diaphragm type, wherein it is desirable to employ low pressure diaphragm assemblies and also to keep the diaphragm diameter and valve size small. In the slide valves heretofore employed, the cooperating valve sealing surfaces are flat and have large frictional resistance because of the extensive contacting surface areas. Therefore, a relatively large shifting force is required. In the case of diaphragm valve assemblies, relatively large-area diaphragms and relatively high shifting fluid pressures are required.
Examples of typical designs previously employed in the prior art are illustrated in the following prior U.S. patents, found in a preliminary search, which appear to show the present state of the art:
Hartman, -- U.S. Pat. No. 3,610,574 PA1 Armstrong, -- U.S. Pat. No. 3,661,357 PA1 Davis, -- U.S. Pat. No. 3,773,082 PA1 Commarmot, -- U.S. Pat. No. 3,674,236 PA1 Dietzsch, 13 U.S. Pat. No. 3,933,339 PA1 Bauman, -- U.S. Pat. No. 3,955,591